这一段是什么意思？为什么字节数组里面要放8*1024

FileInputStream in=new FileInputStream(srcFile);
            FileOutputStream out=new FileOutputStream(desFile);
            byte[] suo=new byte[8*1024];
            int b;
            while((b=in.read(suo,0,suo.length))!=-1){
                out.write(suo, 0, b);
                out.flush();
            }