The System Unit
A point of contention between Creative and IBM prior to my visit to Boca Raton was that IBM would not allow the cover to be removed from the unit until after the first customer shipment in October. I was delighted to receive permission to take my peek on the grounds that this article would be published well after the machine was in the hands of the public. I can therefore tell you that inside the system unit there are a bunch of green cards full of little black things with lots of silver legs.
The system unit sans cover is surprisingly compact. Viewed from the top,
the power supply occupies about an eighth of the space in the rear right
corner. It is completely enclosed in steel, with an intake fan mounted
directly under the top. I had not seen a fuse from the outside and none were
in evidence inside; the power supply has an internal circuit breaker which
resets automatically after ten or so seconds. The two diskette drives are
mounted in the front of the cabinet and extend to within an inch of the
power supply. Together, both drives and the power supply take up about 2/3
of the space inside. A small speaker is mounted on the left side of the
chassis near the front an is connected to the main board with a plug.
The CPU card is mounted flat on the bottom of the chassis and extends from front to back on the left side. One corner of the board is hidden under the diskette drives. To the rear are five slot connectors into which adapter cards for the various peripherals are inserted. The slots are numbered 1 to 5 from left to right, and line up directly with five holes cut into the rear of the chassis. If the slot has no card inserted, the rear panel hole for that slot is covered with a small metal cover which is attached with a screw to the rear panel. This cover is discarded for slots to be filled, since each card is permanently attached to such a cover, through which the necessary external connectors protrude. With the card inserted and the cover screwed down, the card is held rigidly in place. The IBM designers have solved three problems in one with this clever scheme: the rear panel is clean, and completely sealed; the external connectors are firmly mounted and supported; and the adapter cards are appropriately secured.
Even though all slots are created equal electrically, allowing any adapter card to be used in any slot, IBM recommends that the display adapter card be inserted in slot 2. It turns out that display cards are as long as cards can be in the system unit, and that slot 2 is equipped with a special plastic guide to prevent the long cards from wobbling. In response to my question "Why not guides for all the slots?" IBM replied that it represented additional manufacturing process. Each slot has the holes that support the guides, so the guide in slot 2 can be moved and additional guides could be added.
The Intel 8088 CPU is placed in a socket on the right rear corner of the board. Right next to it is an empty 40-pin socket. IBM in Boca Raton "refused to speculate" about the purpose of the socket but two other sources within IBM stated that it was for future inclusion of an Intel 8087 floating point processor (see box). The CPU board also contains 40kb (kilobytes) of ROM (read only memory) in five sockets, 16kb of RAM (random access memory) soldered to the board, and sockets for an additional 48kb of RAM. Memory beyond 64kb is added with 32kb or 64kb memory cards which occupy system expansion slots. There is a set of DIP (dual inline package) switches which is used to tell the CPU how many diskette units are installed, among other things. A crystal on the CPU card generates a frequency of 14.31Mhz which is divided by 3 to get a 4.77Mhz clock for the CPU, by 4 to get a 3.57Mhz clock to drive television sets, and by 1 to drive direct drive monitors.
I'm not an engineer. To my eye, all the boards seemed well constructed. There seemed to be good separation between components and between tracks. The adapter card slots were well-spaced so cards should not touch and air circulation should not be impeded. The chassis and the cover are both steel and the entire unit is well sealed. The system has received FCC Class B certification for home computers and is UL approved.
The 40kb of ROM that comes with every system unit contains three software elements. 2kb is devoted to diagnostics which perform comprehensive tests of the entire system, including memory, whenever the system is turned on or the ALT-CTRL-DEL key combination is depressed. 6kb is IBM's Basic Input/Output System (BIOS) which provides control for all devices except diskette drives. The remaining 32kb is a Basic language interpreter which IBM calls Cassette Basic and which is automatically started if there is not a disk in the diskette drive or if there is not a diskette drive.
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