by
Anonymous Coward
on 2013年04月29日 4時19分
(#2372263)
Z80のインデックスレジスタを上下半分ずつ使えるのは設計者のプライドの問題だったそうで
http://archive.computerhistory.org/resources/access/text/Oral_History/... [computerhistory.org] 9/21ページの下のほうから > . So I introduced a unique design technology as follows: At first in order to expand the number of instruction set with small number of transistors I introduced two prefix in the > instruction. One for index register X, one for the index register Y. If the prefix instruction was added to certain instruction, including the old 8080 instruction, and the new instruction set, the prefix instruction is able to redirect the selection of each register to index register X or Y. And this was our pride for not only 16-bit index register, but also the lower or higher of index register. But we didn’t publish that one.
63ビットもアドレスはいらない (スコア:0)
48ビットで十分ですよ
Re: (スコア:0)
68Kの悪口？ 大きさは半分ですけど。
アドレスデータの上位ビットは、別のデータを入れる領域です(キリッ
Re: (スコア:0)
その反省にたって、AMD64では未定義の上位ビットを使おうとすると例外が飛びます。
Z80には「未定義命令」とかいう裏技が存在したけど最近は無効命令例外を投げるだけになったみたいなものですね。
Re:63ビットもアドレスはいらない (スコア:0)
Z80のインデックスレジスタを上下半分ずつ使えるのは設計者のプライドの問題だったそうで
http://archive.computerhistory.org/resources/access/text/Oral_History/... [computerhistory.org]
9/21ページの下のほうから
> . So I introduced a unique design technology as follows: At first in order to
expand the number of instruction set with small number of transistors I introduced two prefix in the
> instruction. One for index register X, one for the index register Y. If the prefix instruction was added to
certain instruction, including the old 8080 instruction, and the new instruction set, the prefix instruction is
able to redirect the selection of each register to index register X or Y. And this was our pride for not only
16-bit index register, but also the lower or higher of index register. But we didn’t publish that one.