Community hub
Recent from talks
Contribute something to knowledge base
Content stats: 0 posts, 0 articles, 0 media, 0 notes
Members stats: 0 subscribers, 0 contributors, 0 moderators, 0 supporters
Subscribers
Supporters
Contributors
Moderators
Hub AI
PC-based IBM mainframe-compatible systems AI simulator
(@PC-based IBM mainframe-compatible systems_simulator)
Hub AI
PC-based IBM mainframe-compatible systems AI simulator
(@PC-based IBM mainframe-compatible systems_simulator)
PC-based IBM mainframe-compatible systems
Since the rise of the personal computer in the 1980s, IBM and other vendors have created PC-based IBM mainframe-compatible systems which are compatible with the larger IBM mainframe computers. For a period of time PC-based mainframe-compatible systems had a lower price and did not require as much electricity or floor space. However, they sacrificed performance and were not as dependable as mainframe-class hardware. These products have been popular with mainframe developers, in education and training settings, for very small companies with non-critical processing, and in certain disaster relief roles (such as field insurance adjustment systems for hurricane relief).
Up until the mid-1990s, mainframes were very large machines that often occupied entire rooms. The rooms were often air conditioned and had special power arrangements to accommodate the three-phase electric power required by the machines. Modern mainframes are now physically comparatively small and require little or no special building arrangements.
IBM had demonstrated use of a mainframe instruction set in their first desktop computer—the IBM 5100, released in 1975. This product used microcode to execute many of the System/370's processor instructions, so that it could run a slightly modified version of IBM's APL mainframe program interpreter.
In 1980 rumors spread of a new IBM personal computer, perhaps a miniaturized version of the 370. In 1981 the IBM Personal Computer appeared, but it was not based on the System 370 architecture. However, IBM did use their new PC platform to create combinations with additional hardware that could execute S/370 instructions locally.
In October 1983, IBM announced the IBM Personal Computer XT/370. This was essentially a three-in-one product. It could run PC DOS locally, it could also act as 3270 terminal, and finally—its most important distinguishing feature relative to an IBM 3270 PC—was that it could execute S/370 instructions locally.
The XT/370 was an IBM Personal Computer XT (System Unit 5160) with three custom 8-bit cards. The processor card (370PC-P), contained two modified Motorola 68000 chips (which could emulate most S/370 fixed-point instructions and non-floating-point instructions), and an Intel 8087 coprocessor modified to emulate the S/370 floating point instructions. The second card (370PC-M), which connected to the first with a unique card back connector contained 512 KiB of memory. The third card (PC3277-EM), was a 3270 terminal emulator required to download system software from the host mainframe. The XT/370 computer booted into DOS, then ran the VM/PC Control Program. The card's memory space added additional system memory, so the first 256 KiB (motherboard) memory could be used to move data to the 512 KiB expansion card. The expansion memory was dual ported, and provided an additional 384 KiB to the XT Machine bringing the total RAM on the XT side to 640 KiB. The memory arbitrator could bank switch the second 128 KiB bank on the card to other banks, allowing the XT Intel 8088 processor to address all the RAM on the 370PC-M card. Besides the 416 kB of usable RAM for S/370 applications, the XT/370 also supported up to 4 MB of virtual memory using the hard drive as its paging device.
IBM claimed the XT/370 reached 0.1 MIPS (when the data fit in RAM). In 1984, the list price of an XT/370 in its typical configuration was approximately $12,000 so compared favorably with IBM's own mainframes on a $/MIPS basis; for example, an IBM 4341 delivered 1.2 MIPS for $500,000. While it theoretically reduced demand on customers' mainframes by offloading load onto the smaller computer, as customers purchased more XT/370s they likely increased the overall load on the mainframes, increasing IBM's mainframe sales.
Similarly to the mainframe version of VM/CMS, the VM/PC also created the illusion of virtual disks, but on the PC version these were maintained as PC DOS files, either on floppy or hard disk. For example, the CMS virtual disk belonging to user FRED at device address 101 was stored as the DOS file FRED.101. The CMS IMPORT and EXPORT commands allowed extraction of files from these virtual drives as well as ASCII/EBCDIC conversion.
PC-based IBM mainframe-compatible systems
Since the rise of the personal computer in the 1980s, IBM and other vendors have created PC-based IBM mainframe-compatible systems which are compatible with the larger IBM mainframe computers. For a period of time PC-based mainframe-compatible systems had a lower price and did not require as much electricity or floor space. However, they sacrificed performance and were not as dependable as mainframe-class hardware. These products have been popular with mainframe developers, in education and training settings, for very small companies with non-critical processing, and in certain disaster relief roles (such as field insurance adjustment systems for hurricane relief).
Up until the mid-1990s, mainframes were very large machines that often occupied entire rooms. The rooms were often air conditioned and had special power arrangements to accommodate the three-phase electric power required by the machines. Modern mainframes are now physically comparatively small and require little or no special building arrangements.
IBM had demonstrated use of a mainframe instruction set in their first desktop computer—the IBM 5100, released in 1975. This product used microcode to execute many of the System/370's processor instructions, so that it could run a slightly modified version of IBM's APL mainframe program interpreter.
In 1980 rumors spread of a new IBM personal computer, perhaps a miniaturized version of the 370. In 1981 the IBM Personal Computer appeared, but it was not based on the System 370 architecture. However, IBM did use their new PC platform to create combinations with additional hardware that could execute S/370 instructions locally.
In October 1983, IBM announced the IBM Personal Computer XT/370. This was essentially a three-in-one product. It could run PC DOS locally, it could also act as 3270 terminal, and finally—its most important distinguishing feature relative to an IBM 3270 PC—was that it could execute S/370 instructions locally.
The XT/370 was an IBM Personal Computer XT (System Unit 5160) with three custom 8-bit cards. The processor card (370PC-P), contained two modified Motorola 68000 chips (which could emulate most S/370 fixed-point instructions and non-floating-point instructions), and an Intel 8087 coprocessor modified to emulate the S/370 floating point instructions. The second card (370PC-M), which connected to the first with a unique card back connector contained 512 KiB of memory. The third card (PC3277-EM), was a 3270 terminal emulator required to download system software from the host mainframe. The XT/370 computer booted into DOS, then ran the VM/PC Control Program. The card's memory space added additional system memory, so the first 256 KiB (motherboard) memory could be used to move data to the 512 KiB expansion card. The expansion memory was dual ported, and provided an additional 384 KiB to the XT Machine bringing the total RAM on the XT side to 640 KiB. The memory arbitrator could bank switch the second 128 KiB bank on the card to other banks, allowing the XT Intel 8088 processor to address all the RAM on the 370PC-M card. Besides the 416 kB of usable RAM for S/370 applications, the XT/370 also supported up to 4 MB of virtual memory using the hard drive as its paging device.
IBM claimed the XT/370 reached 0.1 MIPS (when the data fit in RAM). In 1984, the list price of an XT/370 in its typical configuration was approximately $12,000 so compared favorably with IBM's own mainframes on a $/MIPS basis; for example, an IBM 4341 delivered 1.2 MIPS for $500,000. While it theoretically reduced demand on customers' mainframes by offloading load onto the smaller computer, as customers purchased more XT/370s they likely increased the overall load on the mainframes, increasing IBM's mainframe sales.
Similarly to the mainframe version of VM/CMS, the VM/PC also created the illusion of virtual disks, but on the PC version these were maintained as PC DOS files, either on floppy or hard disk. For example, the CMS virtual disk belonging to user FRED at device address 101 was stored as the DOS file FRED.101. The CMS IMPORT and EXPORT commands allowed extraction of files from these virtual drives as well as ASCII/EBCDIC conversion.