IBM Cassette BASIC: Difference between revisions

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The '''IBM Cassette BASIC''' ~~(officially '''IBM BASIC C1.0''', later C1.1)~~ is the ~~32 KB ROM-resident~~ Microsoft BASIC supplied in every [[IBM PC (5150)]] and [[IBM PC XT (5160)]] motherboard. It lives in ~~the four~~ sockets U29, U30, U31, U32 on the 5150 board, and is automatically launched by the BIOS when no boot disk is found in drive A ~~and no Disk BASIC overlay is loaded~~.

The '''IBM Cassette BASIC''' is the Microsoft BASIC supplied in ROM on every [[IBM PC (5150)]] and [[IBM PC XT (5160)]] motherboard. It lives in sockets U29, U30, U31, U32 on the 5150 board, and is automatically launched by the BIOS when no boot disk is found in drive A.

== History ==

Cassette BASIC was written by Microsoft for IBM as part of the original PC project ~~("Project Chess")~~. The version in the first 5150 ROMs is '''C1.0''', dated 1981; a later revision '''C1.1''' shipped in machines built from late 1982 onward and was retained throughout the 5160 production run. C1.1 fixes several bugs in the floating-point library and adds support for the 8087 FPU when present.

Cassette BASIC was written by Microsoft for IBM as part of the original PC project. The same ROM image was supplied unchanged on the 5160 XT and on early 5170 AT machines. It was dropped from the [[IBM PCjr]] and the later PS/2 line.

The same ROM image was supplied unchanged on the 5160 XT and on early 5170 AT machines~~; it~~ was ~~finally~~ dropped from the [[IBM PCjr]] and the later PS/2 line.

== ROM Layout ==

* '''U29''' — 8 KB ROM, BASIC ~~pages 0~~

The 5150 motherboard carries Cassette BASIC in four sockets:

* '''U30''' — 8 KB ROM, BASIC pages 1

* '''U31''' — 8 KB ROM, BASIC pages 2

* '''U32''' — 8 KB ROM, BASIC pages 3

~~The four 24-pin DIP ROMs are part-marked with their IBM dash numbers and a 5700xxxx-series part number~~ (~~C1.0) or a 1501xxx-series part number (C1.1~~).

* '''U29, U30, U31, U32''' — Cassette BASIC ROM (BIOS lives separately in U33).

== Disk Variants ==

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* '''"BASIC ROM" missing or corrupt''' — POST passes but the BASIC banner is garbled or BASIC will not start. Reseat U29-U32, then swap each ROM with a known-good donor to identify the failed chip.

* ~~'''"NL~~/~~CR" sequence prints garbage''' — the 8255 PPI keyboard interface or a bad parity bit; usually a separate fault from BASIC itself~~.

* '''CASSAVE / ~~CLOAD failures''' — the cassette port~~ on the 5150 ~~has been functionally abandoned for decades; verify the −5 V rail before chasing the cassette circuitry~~.

== References ==

* [https://minuszerodegrees.net/5150/basic/5150_cassette_basic.htm Cassette BASIC on the 5150], minuszerodegrees.net.

== Related Pages ==

@@ Line 1: / Line 1: @@
-The '''IBM Cassette BASIC''' (officially '''IBM BASIC C1.0''', later C1.1) is the 32 KB ROM-resident Microsoft BASIC supplied in every [[IBM PC (5150)]] and [[IBM PC XT (5160)]] motherboard. It lives in the four sockets U29, U30, U31, U32 on the 5150 board, and is automatically launched by the BIOS when no boot disk is found in drive A and no Disk BASIC overlay is loaded.
+The '''IBM Cassette BASIC''' is the Microsoft BASIC supplied in ROM on every [[IBM PC (5150)]] and [[IBM PC XT (5160)]] motherboard. It lives in sockets U29, U30, U31, U32 on the 5150 board, and is automatically launched by the BIOS when no boot disk is found in drive A.
 == History ==
-Cassette BASIC was written by Microsoft for IBM as part of the original PC project ("Project Chess"). The version in the first 5150 ROMs is '''C1.0''', dated 1981; a later revision '''C1.1''' shipped in machines built from late 1982 onward and was retained throughout the 5160 production run. C1.1 fixes several bugs in the floating-point library and adds support for the 8087 FPU when present.
+Cassette BASIC was written by Microsoft for IBM as part of the original PC project. The same ROM image was supplied unchanged on the 5160 XT and on early 5170 AT machines. It was dropped from the [[IBM PCjr]] and the later PS/2 line.
-The same ROM image was supplied unchanged on the 5160 XT and on early 5170 AT machines; it was finally dropped from the [[IBM PCjr]] and the later PS/2 line.
 == ROM Layout ==
-* '''U29''' — 8 KB ROM, BASIC pages 0
+The 5150 motherboard carries Cassette BASIC in four sockets:
-* '''U30''' — 8 KB ROM, BASIC pages 1
-* '''U31''' — 8 KB ROM, BASIC pages 2
-* '''U32''' — 8 KB ROM, BASIC pages 3
-The four 24-pin DIP ROMs are part-marked with their IBM dash numbers and a 5700xxxx-series part number (C1.0) or a 1501xxx-series part number (C1.1).
+* '''U29, U30, U31, U32''' — Cassette BASIC ROM (BIOS lives separately in U33).
 == Disk Variants ==
@@ Line 37: / Line 32: @@
 * '''"BASIC ROM" missing or corrupt''' — POST passes but the BASIC banner is garbled or BASIC will not start. Reseat U29-U32, then swap each ROM with a known-good donor to identify the failed chip.
-* '''"NL/CR" sequence prints garbage''' — the 8255 PPI keyboard interface or a bad parity bit; usually a separate fault from BASIC itself.
-* '''CASSAVE / CLOAD failures''' — the cassette port on the 5150 has been functionally abandoned for decades; verify the &minus;5 V rail before chasing the cassette circuitry.
+== References ==
+* [https://minuszerodegrees.net/5150/basic/5150_cassette_basic.htm Cassette BASIC on the 5150], minuszerodegrees.net.
 == Related Pages ==

IBM Cassette BASIC: Difference between revisions

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