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Certificates are (1) documents attesting to the (2) of a public key to an individual or other entity. They allow verification of the claim that a given public key does in fact belong to a given individual. Certificates help prevent someone from using a phony key to (3)someone else. In their simplest form, Certificates contain a public key and a name. As commonly used, a certificate also contains an (4)date, the name of the CA that issued the certificate, a serial number, and perhaps other in
第23题:若计算机系统的字长为128位,磁盘的容量为2048GB,物理块的大小为8MB,假设文件管理系统采用位示图(bitmap)法记录该计算机系统磁盘的使用情况,那么位示图的大小需要( )个字。 若有关系模式R(A,B,C)和S(C,D,E),对于如下的关系代数表达式:
E=∏A,D(σB<'2003'∧R.C=S.C∧E='80'(R×S))
E=∏A,D(σR.C=S.C(σB<'2003'(R)×σE='80'(S)))
E=∏A,D(σB<'2003'(R) σE='80'(S))
E=∏A,D(σB<'2003'∧E='80'(R S))
正确的结论是(1),表达式 (2)的查询效率最高。
(1)A、E1≡E2≡E3≡E4
B、E3≡E4但E1≠E2
C、E1&equiv
()不是 RISC 的特点。
A.指令种类丰富
B.高效的流水线操作
C.寻址方式较少
D.硬布线控制