Chúng tôi sẽ xem xét một số phương pháp của bộ nhớ đệm xem có thể loại bỏ các yêu cầu năng động hoàn toàn. Rails cung cấp ba cấp độ khác nhau của bộ nhớ đệm xem, đều có ưu và khuyết điểm riêng của mình. Mặc dù bộ nhớ đệm trang cung cấp cho bạn những lợi ích hiệu suất lớn nhất, nó cũng là khó khăn nhất để quản lý. | 51 binary multiplication The advantage of BCD shows up when a number has a fractional part such as . There is no way to convert into binary exactly it would require an infinite number of digits just like converting 3 into decimal see ROUNDING error . But in BCD is represented by the code for 1 immediately after the point and no accuracy is lost. BCD arithmetic is considerably slower and takes more memory than binary arithmetic. It is used primarily in financial work and other situations where rounding errors are intolerable. Pocket calculators use BCD. FIGURE 31. Binary addition half adder FIGURE 32. Binary addition full adder binary file a file containing bits or bytes that do not necessarily represent printable text. The term binary file usually denotes any file that is not a text file such as executable machine language code. Crucially special software is required to print a binary file or view it on the screen. Contrast TEXT FILE. binary multiplication a basic operation in computer arithmetic. For singledigit numbers the binary multiplication table is very simple and is the same as the Boolean AND operation see AND GATE 0 X 0 0 0 X 1 0 1 X 0 0 1 X 1 1 For numbers with more than one digit the computer does something very similar to what we do to decimal numbers in pencil-and-paper arithmetic. To find 13 X 21 in decimal we proceed like this binary number 52 21 X 13 63 21 27ã First find 3 X 21. Then find 10 X 21 and add these two results together to get the final product. Note that the product has more digits than either of the two original numbers. You can follow the same procedure to multiply two binary numbers 10101 X01101 10101 00000 10101 10101 00000 100010001 Notice that each of the partial products is either zero or a copy of 10101 shifted leftward some number of digits. The partial products that are zero can of course be skipped. Accordingly in order to multiply in binary the computer simply starts with 0 in the accumulator and works through the
