IBM 3350 direct access storage

  • Models A2, A2F, B2 & B2F announced July 15, 1975 and withdrawn September 5, 1994

  • Models C2 and C2F announced November 4, 1975 and withdrawn September 5, 1994
Known during its development as "Madrid," the IBM 3350 was introduced in 1975 and first delivered the following year. It extended Winchester technology by increasing the number of disks per drive and the recording density to provide a 4.5 times increase in capacity per spindle. In addition, the developers eliminated the customer-removable disk pack and circled back to fixed disks, as in the IBM RAMAC, to achieve higher recording densities and lower cost per bit of online storage. In addition, the elimination of operator handling -- and exposure to external contamination -- provided high reliability.
The 3350 furnished a maximum storage capacity of approximately 317.5MB per drive (635MB per unit), allowing more than 2.5 billion bytes of online storage per 3350 string. The data rate was 1198K/second and average seek time was 25 milliseconds.
The 3350 Models A2F and B2F provided 1,144,140 bytes of zero seek time storage per spindle (2,288,280 per unit) when operating in 3350 native mode. Models A2 and A2F were two-drive units with associated controls, which attached to the IBM System/370 Models 135, 155-II and 165-II via the 3830 Model 2, and to the IBM System/370 Model 145, 158 and 168 via their ISCs and/or the 3830 Model 2. The 3350 Models B2 and B2F were two-drive units which attached to the 3350 Model A2 or A2F. Up to three B2 or B2F units could be attached to each A2 or A2F unit, for a maximum of eight drives per 3350 string.
Average seek time (ms): 25
Average rotational delay (ms): 8.4
Data Rate (KB/sec.): 1198
Bytes per track: 19,069
Tracks per logical cylinder: 30
Logical cylinders per drive: 555
Capacity per drive (MB) approx. 317.5
  • Rotational position sensing, which permitted improved block multiplexer channel utilization.

  • Error correction of single data error bursts of up to four bits.

  • Command retry, which enabled the storage control to recover from certain subsystem errors without recourse to system error recovery procedures.

  • Read only switch, gave increased data security by providing for each drive the means to protect data from being overwritten or erased.


IBM 3340

  • Models A2, B1 and B2 announced March 13, 1973

  • Models B1 and C2 withdrawn December 20, 1983

  • Models A2 & B2 withdrawn May 1, 1984
Following a development effort that began in the summer of 1969, the IBM 3340 disk unit was introduced in March 1973 with an advanced disk technology known as "Winchester."* The first 3340 shipments to customers began in November 1973.
The 3340 featured a smaller, lighter read/write head that could ride closer to the disk surface -- on an air film 18 millionths of an inch thick -- with a load of less than 20 grams. The Winchester disk file's low-cost head-slider structure made it feasible to use two heads per surface, cutting the stroke length in half. The disks, the disk spindle and bearings, the carriage and the head-arm assemblies were incorporated into a removable sealed cartridge called the IBM 3348 Data Module. A track density of 300 tracks per inch and an access time of 25 milliseconds were achieved.
The 3340 offered the optional availability of fixed heads, which provided an average access time of only five milliseconds. It had three types of data modules: 35 megabytes, 70 megabytes, and 70 megabytes of which 0.5 megabyte were accessible with fixed heads.
Two-to-four 3340 drives could be attached to the IBM System/370 Model 115 processor -- which had been announced concurrently with the 3340 -- providing a storage capacity of up to 280 million bytes.
* Some observers have noted that the 3340 was known as "Winchester" because its development engineers called it a "30-30" (its two spindles each had a disk capacity of 30 megabytes), the common name of a rifle manufactured by the Winchester Company. Kenneth E. Haughton, who led the 3340 development effort, is reported to have said: "If it's a 30-30, then it must be a Winchester." A new direction
At IBM, we've put our heads together to bring you something new and different in direct access storage devices ... something that utilizes an innovative design approach to give you new data reliability, flexibility, and performance at a price in line with your data processing budget.
It's the IBM 3340 Direct Access Storage Facility, a growth file for those currently operating with IBM 2311s and 2314s. The 3340's innovative design approach is incorporated in its storage media, the IBM 3348 Data Modules. Resembling the familiar disk packs used with other IBM storage devices, the 3348 Data Module is the disk pack's technological successor. For the 3348 contains not only the disk surfaces used for data recording, but the read/write heads and access arms as well.
A happy combination
Why all in one? Because combining them into a single integrated unit can give you greater data reliability than you may have thought possible to achieve with a disk storage device. That's because the write head that records the data on the 3340's disk surfaces is always the read head that reads the data back into your computer. Thus, problems resulting from mistracking due to minute read/write head misalignments are no longer a factor. It is this new Data Module design concept that gives the 3340 greater data reliability and configuration flexibility than offered by any other IBM disk storage unit.
The 3340 also includes several other outstanding features that enhance its read/write reliability. Error correction code in the controller can automatically correct a single loss of data up to three bits long in any data record. Detailed error logging procedures also are included that can help detect potential problems in time for your IBM Customer Engineer to correct them before they become serious.
Advanced features like these give the 3340 the reliability you need to put your critical applications online ... with confidence.
Easy growth at any time
The 3340's range of flexibility in storage capacity is the result of two sizes in Data
Model 35 - 34.9 million bytes, and
Model 70 - 69.8 million bytes.
Both Data Modules are interchangeable and can be used on the same drive without modification. Thus, you can configure your disk subsystem to match your current needs ... and as these needs change, you simply increase the size of the Data Modules to arrive at the desired capacity. It's really simple to keep up with changing storage requirements when you have an IBM 3340!
Performance belies its cost
The performance of the 3340 more than measures up to its advanced design features. In fact, present users of 2311s and 2814s can now move into a level of disk performance that was previously available to them only with IBM's super disk system, the 3330-series. And they can get this kind of performance without having to pay for more storage capacity than they actually need. Check these performance characteristics:
Average seek time (MS)
Average latency (MS)
Data rate (KB/sec.)
Note how much more performance the 3340 offers over that of the 2314. Take a look, too, at how well it stacks up against the 3330. This chart, better than words, indicates the kind of performance you can expect from this outstanding disk file. In fact, in the average computer installation, the 3340 should provide performance very close to that of a 3330... at a price well within the budget range of 2311 and 2314 users.
Rotation Position Sensing (RPS) also is available as an optional feature to boost system throughput. On a 3340 equipped with RPS, one drive can be reading or writing and all other drives in the subsystem can be simultaneously seeking or searching. This capability can significantly enhance system performance, particularly for those systems utilizing large disk subsystems and a high degree of multiprogramming.
Operation is extra easy
The IBM 3340 is probably the easiest-to-operate disk storage device you'll encounter.
To mount a 3348 Data Module, you simply place it in the drive. Its cover need not be removed, nor must it be attached to the drive like previous IBM disk subsystems.
Once the Module is in place, the entire mounting operation is handled automatically by the drive itself. This can result in considerable savings in operator time as well as better utilization of your computing resources.
The particular model being used is automatically sensed and recognized by the 3340. This eliminates need for either the computer operator or the programmer to specify the model in use, and, generally, no program changes are required to accommodate the various models.
Once the disks are brought up to speed, the 3340 is ready for processing to begin. Time for the entire mounting operation: less than 20 seconds!
Use it with all VS System/370s
The 3340 can be used with all System/370 models utilizing DOS/VS, OS/VS1, or Release 2 of 05/ VS2. It's economical enough to fit into the plans of the smallest System/370 user, yet it offers more than enough performance to function efficiently with the models at the top of the line. The new file uses the same integrated attachments as the 3330.
Configuration flexibility
With System/370 Models 115 and 125, the 3340 is directly attached, while with the Model 135, it attaches to the 3330/3340 Integrated File Adapter (IFA). With the Model 145, attachment is through either the Integrated Storage Control (ISC) feature or the 3345 Storage and Control Frame Models 3, 4, and 5. With Model 158 or 168 attachment is through the ISC. In addition, the 3340 can attached to all VS System/370s the Model 135 up via the 3830 Storage Control Model 2.
Also on the Model 135 and larger VS System/370s, a new intermix capability permits 3340s and 3330s to be used together on the same attachment. And with these same systems, use of the optional String Switch Feature allows 3340 strings consisting of up to eight drives each to be manually or dynamically switched between any two attachments. Under OS/VS, the optional 32 Drive Expansion Feature increases to 32 the number of drives that can be attached to the 3830 Model 2 or the Model 145's ISC. Also with this feature, the Model 158 and 168 ISCs can control up to 64 drives. These features and channel switches can be used together to provide large storage pools with high subsystem availability.
Get ahead of the pack
Just as System/370 with virtual storage has opened up new application areas that demand more performance and reliability from a direct access storage subsystem, so, too, does the 3340 offer a file that's particularly suited to this advanced computing environment.
The 3340 brings 3330-like performance into the price realm and capacity range of the 2311 and 2314 user. Performance enough to meet the demands of increased multiprogramming, paging, and online applications. Capacity enough to put the bulk of your direct access files online, thus making your data readily accessible, reducing pack changing, and building a firm foundation for your advanced applications.
Now's the time to move up to the IBM 3340 Direct Access Storage Facility. We've gotten our heads together and put it ahead of the pack.


IBM 3330

The IBM 3330 Direct Access Storage Facility, code-named Merlin, was introduced in June 1970 for use with the IBM System/370 and the IBM System 360/195. Its removable disk packs held 100 MB (404x19x13,030 bytes) (the 1973 Model 11 featured IBM 3336-11 Disk Packs that held 200 MB (808x19x13,030 bytes)). Access time was 30 ms and data transferred at 806 kB/s. A major advance introduced with the 3330 was the use of error correction, which made the drives more reliable and reduced costs because small imperfections in the disk surface could be tolerated. The circuitry could correct error bursts up to 11 bits long. The 3330 was withdrawn in 1983.